The vast majority of audio transducers employ cylindrical diaphragms formed from flat sheets that are curved so that all lines normal to the curved surface remain perpendicular to the longitudinal axis of the diaphragm. Although such transducers are most common, there are many other forms of acoustic energy generating devices such as those disclosed in International Publication No. WO93-23967 and U.S. Pat. No. 5,249,237.
A significant departure from those diaphragms created from flat sheets are those disclosed in U.S. Pat. No. 6,061,461, the disclosure of which is incorporated by reference herein. Transducers disclosed in the '461 patent are especially useful as high frequency or tweeter transducers that are not necessarily limited to the reproduction of high frequencies. These transducers include a rigid frame and a permanent ring magnet mounted to the frame and a small bobbin, preferably formed of aluminum foil sized and arranged to fit within the open end of a magnetic gap while providing motion of the bobbin therein. A voice coil is wound on the bobbin and connectable to receive an audio signal similar to a conventional voice coil driver system. What is unique to the '461 patented invention is the use of flexible, curved diaphragms disposed in a frame generally free to move except for the distal end of each diaphragm which is fixed to the frame of the transducer. The proximal ends of the diaphragms are connected together in a spaced relationship by a pliable decoupling pad, preferably formed of a closed-cell foam tape for decoupling the diaphragms from one another while enabling them to be driven with a single voice coil driver assembly.
Although the transducers described in the '461 patent provide excellent high frequency response and dispersion of acoustic energy, such transducers are not free of faults. In sum, the transducer to be described herein constituting the present invention is capable of smooth amplitude-frequency response, high electro acoustic conversion efficiency, wide dispersion of sound output and low distortion. Transducers of the present invention when operated above approximately 2 kHz represent a marked improvement over direct-radiator transducers which employ rigid diaphragms and are therefore, by necessity, very small. At high amplitudes the rigidity of such diaphragms usually fail in unpredictable modes and the result is non-uniform response in both amplitude and dispersion. As was the case with the '461 transducer, the present invention makes use of the propagation of bending waves in a non-rigid material. In this type of transducer, the properties of the diaphragm material are exploited rather than design limitations to be overcome.